Field of the Invention
Example embodiments relate generally to a system and method for determining cell congestion using an average physical resource block rate.
Related Art
FIG. 1 is a conventional network 10 with mobile User Equipment (UE) 110 connected to the Internet Protocol (IP) Packet Data Network (IP-PDN) 1001 (also referred to as internet) wirelessly via 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE) IP Connectivity Network (IP-CAN) 100 (also referred to as a wireless network). The IP-CAN 100 generally includes: a serving gateway (SGW) 101; a packet data network (PDN) gateway (PGW) 103; a policy and charging rules function (PCRF) 106; a mobility management entity (MME) 108, and an Evolved Node B (eNB) 105 (also referred to as cell). The IP-PDN 1001 includes Application Function (AF) 109 which may include application or proxy servers, media servers, email servers, other connected UEs, etc.
Within the IP-CAN 100, the eNB 105 is part of what is referred to as an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (EUTRAN), and the portion of the IP-CAN 100 including the SGW 101, the PGW 103, and the MME 108 is referred to as an Evolved Packet Core (EPC). Although only a single eNB 105 is shown in FIG. 1, it should be understood that the EUTRAN may include any number of eNBs. Similarly, although only a single SGW, PGW and MME are shown in FIG. 1, it should be understood that the EPC may include any number of these core network elements.
The eNB 105 provides wireless resources and radio coverage for UEs including UE 110. For the purpose of clarity, only one UE is illustrated in FIG. 1. However, any number of UEs may be connected (or attached) to the eNB 105. The eNB 105 is operatively coupled to the SGW 101 and the MME 108.
The SGW 101 routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNB handovers of UEs. The SGW 101 also acts as the anchor for mobility between 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE) and other 3GPP technologies. For idle UEs, the SGW 101 terminates the downlink data path and triggers paging when downlink data arrives for UEs.
The PGW 103 provides connectivity between the UE 110 and the external packet data networks (e.g., the IP-PDN) by being the point of entry/exit of traffic for the UE 110. As is known, a given UE may have simultaneous connectivity with more than one PGW for accessing multiple PDNs.
The PGW 103 also performs policy enforcement, packet filtering for UEs, charging support, lawful interception and packet screening, each of which are well-known functions. The PGW 103 also acts as the anchor for mobility between 3GPP and non-3GPP technologies, such as Worldwide Interoperability for Microwave Access (WiMAX) and 3rd Generation Partnership Project 2 (3GPP2 (code division multiple access (CDMA) 1× and Enhanced Voice Data Optimized (EvDO)).
Still referring to FIG. 1, the eNB 105 is also operatively coupled to the MME 108. The MME 108 is the control-node for the EUTRAN, and is responsible for idle mode UE paging and tagging procedures including retransmissions. The MME 108 is also responsible for choosing a particular SGW for a UE during initial attachment of the UE to the network, and during intra-LTE handover involving Core Network (CN) node relocation. The MME 108 authenticates UEs by interacting with a Home Subscriber Server (HSS), which is not shown in FIG. 1.
Non Access Stratum (NAS) signaling terminates at the MME 108, and is responsible for generation and allocation of temporary identities for UEs. The MME 108 also checks the authorization of a UE to camp on a service provider's Public Land Mobile Network (PLMN), and enforces UE roaming restrictions. The MME 108 is the termination point in the network for ciphering/integrity protection for NAS signaling, and handles security key management.
The MME 108 also provides control plane functionality for mobility between LTE and 2G/3G access networks with the S3 interface from the SGSN (not shown) terminating at the MME 108.
The Policy and Charging Rules Function (PCRF) 106 is the entity that makes policy decisions and sets charging rules. It has access to subscriber databases and plays a role in the 3GPP architecture as specified in 3GPP TS 23.303 “Policy and Charging Control Architecture”. In particular PCRF via PGW may configure wireless bearers, and PCRF also may configure policies on PGW and SGW related to flow control of the packets that belong to a particular bearer.
UE 110 communicates with the Application Function (AF) 109 via IP-CAN 100 to establish application session, receive and send application content and other application specific information. AF 109 may be a server in IP-PDN, or a peer end user device or a combination of these. AF 109 may register with PCRF 106 to receive application level policy that may enable adapting application behavior to help improve end user quality of experience.
FIG. 2 is a diagram of a conventional E-UTRAN Node B (eNB) 105. The eNB 105 includes: a memory 240; a processor 220; a scheduler 210; and communication interfaces 260. The processor 220 may also be referred to as a core network entity processing circuit, an EPC entity processing circuit, etc. The processor 220 controls the function of eNB 105 (as described herein), and is operatively coupled to the memory 240 and the communication interfaces 260.
The eNB may include one or more cells or sectors serving UEs within individual geometric coverage sector areas. Each cell individually may contain elements depicted in FIG. 2. Throughout this document the terms eNB, cell or sector shall be used interchangeably.
Still referring to FIG. 2, the communication interfaces 260 include various interfaces including one or more transmitters/receivers connected to one or more antennas to transmit/receive (wireline and/or wirelessly) control and data signals to/from UEs or via a control plane or interface to other EPC network elements and/or RAN elements. The scheduler 210 schedules control and data communications that are to be transmitted and received by the eNB 105 to and from UEs 110. The memory 240 may buffer and store data that is being transmitted and received to and from eNB 105.
Every Transmission Time Interval (m), typically equal to 1 millisecond, the scheduler may allocate a certain number of Physical Resource Blocks (PRBs) to different bearers carrying data over the wireless link in the Downlink (from eNB 105 to UE 110) and Uplink (from UE 110 to eNB 105) directions. The scheduler may also determine Modulation and Coding Schema (MCS) that may define how many bits of information may be packed into the allocated number of PRBs. The latter is defined by the 3GPP TS36.213 tables 7.1.7.1-1 and 7.1.7.2.1-1, which presents a lookup table for a number of bits of data that may be included in PRBs sent per TTI for a given allocated number of PRBs and a MCS value. MCS is computed by the scheduler using Channel Quality Indicator (CQI) values reported by the UE 110 that in turn may be derived from measured by the UE 110 wireless channel conditions in the form of Signal to Interference and Noise Ratio (SINR).
Scheduler 210 may make PRB allocation decisions based upon a Quality of Service (QoS) Class Identifier (QCI), which represents traffic priority hierarchy. There are nine QCI classes currently defined in LTE, with 1 representing highest priority and 9 representing the lowest priority. QCIs 1 to 4 are reserved for Guaranteed Bitrate (GBR) classes for which the scheduler maintains certain specific data flow QoS characteristics. QCIs 5 to 9 are reserved for various categories of Best Effort traffic.
While the scheduler operations are not standardized, there are certain generic types of schedulers that are generally accepted. Examples include strict priority scheduler (SPS) and proportional weighted fair share scheduler (PWFSS). Both types try to honor GBR needs first by allocating dedicated resources to meet whenever possible the GBR bearer throughput constraints while leaving enough resources to maintain certain minimal data traffic for non-GBR classes. The SPS allocates higher priority classes with all the resources that may be needed (except for a certain minimal amount of resources to avoid starving lower priority classes), and lower priority classes generally receive the remaining resources. The PWFSS gives each non-GBR QCI class certain weighted share of resources, that may not be exceeded unless unutilized resources are available.
Radio access network (RAN) congestion detection and congestion level determination is critical in order to optimize the network 10 performance of applications. Conventionally, there is not standardized definition of congestion that allows for a simple and measurable way to determine network congestion levels. While 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE) standards currently define various means of reporting RAN congestion levels (see 3GPP TR 23.705 in particular), the definition and computation of “congestion” remains undefined.
Conventional characteristics of cell congestion are often defined in terms of user equipment (UE) throughput, a number of UEs being served, or a percentage of cell load being monopolized/used. However, these measures of cell congestion are inadequate, for some of the reasons described in detail herein.
First, characterization of cell congestion in terms of UE throughput is inadequate because UE throughput in wireless networks is also dependent upon channel conditions of the UE. Cell congestion level describes the state of the available cell resources and therefore should not be dependent upon channel conditions of individual UEs, as movement of UEs may abruptly change the channel conditions.
Second, characterization of congestion level in terms of a number of active UEs being served is an inadequate measure, because many UEs may be passing very light traffic, these UEs with very light traffic will have no significant impact on an amount of throughput that may be available for a UE joining a cell which may have much heavier demands. For this reason, a number of active UEs being served is also not an effective good measure of cell congestion level.
Third, characterization of congestion level in terms of a percentage of cell load being used is inadequate. This is because, in LTE for instance, one or two users may fully load the cell because of a large amount of traffic that these small group of users may be monopolizing due to, for example, downloading or uploading of large files. Because this measure of congestion may be skewed to appear that the network is congested based on the demands of a small group of users, a percentage of cell load being used is also not a good measure of congestion.
In addition to the conventional problems associated with defining congestion, an amount of traffic that a single UE may receive also depends upon the type of application the UE may be using. The definition of cell congestion level should not be dependent upon the application that is being used, but rather the definition should be determined by the availability of cell resources. For example, if a UE is running an application on a best efforts basis, the UE may usurp close to 100% of downlink cell capacity for ftp downloads. However, such network use should not accurately be considered “congested.” This is because, if another UE joins the network and runs an application on a best efforts basis for ftp downloads, this additional user may receive approximately 50% of cell resources due to fairness scheduling by an E-UTRAN Node B (eNodeB), as the network has ample capacity to serve both UE.
Because existing definitions of congestion are ambiguous, standards often times describe what congestion is not, as opposed to what congestion is, and these standards do not describe any specific methods for estimating network congestion level. For example, 3GPP Technical Report (TR) 23.705 includes a study on system enhancements for user plane congestion management indicating that RAN user plane congestion occurs when demand for RAN resources exceeds the available RAN capacity to deliver the user data for a period of time, and congestion leads, for example, to packet drops or delays, and may or may not result in degraded end-user experience. The 3GPP TR further explains that short-duration traffic bursts is a normal condition at any traffic load level, and is not considered to be RAN user plane congestion. Likewise, a high-level of utilization of RAN resources (based on operator configuration) is considered a normal mode of operation and might not be RAN user plane congestion. And, RAN user plane congestion includes user plane congestion that occurs over the air interface (e.g. LTE-Uu), in the radio node (e.g. eNB) and/or over the backhaul interface between RAN and CN (e.g. S1-u).
3GPP TR 23.705 also indicates that a user-impact to congestion occurs when a service that is delivered to a UE over a default bearer or a dedicated bearer does not meet the user's expected service experience due to RAN user plane congestion. The expectation for a service delivery is highly dependent on the particular service or application. The expected service experience may also differ between subscriber groups (e.g., a premium subscriber may have higher expectations than a subscriber with the cheapest subscription). RAN resource shortage where the RAN can still fulfill the user expectations for a service delivery is not considered to be user-impacting congestion; rather, it is an indication for full RAN resource utilization, and as such a normal mode of operation. 3GPP TR 23.705 therefore notes that “It is up to the operator to determine when a service satisfies the user's expected service experience.”